Apparatus for high-frequency induction heating of strips



April 15, 1947. CASSEN ET AL 2,419,116

' APPARATUS FOR HIGH-FREQUENCY INDUCTION HEATING 0F STRIPS Filed April 20, 1944 WITNESSES:

INVENTORS Barred/cf Cassen 6? R0 berf M. Baker Patented Apr. 15, 1947 UNITED STATES PATENT OFFICE APPARATUS FOR HIGH-FREQUENCY INDUCTION HEATING F STRIPS Benedict Cassen, Los Angeles, Calif., and Robert M. Baker, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 20, 1944, Serial No. 531,862

Claims. (01. 219-13) 1, 2

Our invention relates, generally, to induction by varying the distance between the heating coils heating without the use of iron-cores; and, more therefore, with respect to the material being particularly, is in the nature of an improvement heated, thereby affording an easy method for in coreless or air-cored induction heating furnace regulating the power input into the material apparatus for inducing heating electrical cur- 5 without requiring controlling operations on the rents in traveling elongated material, such as tube-oscillator generator or other generating strips, sheets, rods, and the like, by a pulsating power source with which it is desirable to energize magnetic field or fields having magnetic lines the induction heating coils, longitudinally interlinking the material. By Other features, apparatus, means and methods longitudinally, I mean extending generally in the Of Our invention, in addition to the foregoing direction of the length of the material, or on a ay be discernible from the following description li in hi h a at ia m v thereof, to be taken in Connection with the ac- In present apparatus of this kind, elongated flompdnying Schematic d a g. material is inductively heated by longitudinal Inthe drawing: magnetic flux in order automatically to provide Figure 1 s a ia ra atic View of an embodiuniformity of temperature distribution transment of our invention, looking at the face of versely across the moving material, with refera strip being heat-treated; ence to its direction of movement. A helical coil Fig. 2 is a longitud Section, s se to or coils are used for producing this flux. Such Substantially 011 the lines IIII t r f; a coil when energized provides an inner, axial Figs- 8 d 4 re wiring diagrams showin flux; and by passing the material lengthwise manners in which the cooperating heating coils through the inside of the coil, heating of the n o e de f t e s p a e e ect cally material is efiected. A disadvantage of such Cami/acted providing the type of electroma helical heating-coil means resides in the fact 116518 heating of 0111' invention; a d that the elongated material must be threaded i 5 is a per p tive View of a modified form through it, and adjustments in induced power Ofaheating Co l. can not be readily made by changing the inter Referring more rt ul ly to F res 1 and linking of. the magnetic flux with the material 2, the indufition ating furnace apparatus comwhich is centrally inside the coil or coils, prises a pair of similar planar non ag etic air- It is an object of our invention to provide a cored heating coils 2 and 4 parallelly disposed on coreless induction furnace apparatus which can Opposite Sides of a e ing passage 6 be energized with relatively high-frequencies, not through which a relatively Wide and relatively obtainable with common rotating generators, but thin Continuous Strip 3 may be ously passed or moved longitudinally in the direction which will provide satisfactory longitudinal flux induction heating without the use of a helical of its length, for heat-treating the portion moving between the heating coils, Each of the coils coil.

It is another object of our invention to provide is of the flat, pa a e y being pirally Wound with slightly rounded corners.

means for electromagnetically heating elongated Each coil has two groups of active conductors continuously traveling flat material, such as strip, etc., With longitudinal flux obtained Which extend across the Width of the strip, the through the use of two non-magnetic spiralor Conductors in each group being p llel and inpancake-type induction heating coils, each on terconnected by end-turns or end conductors to different side of the material so that it can be complete t e p MOFB p fically, the heatthreaded sidewise or edgewise into the working coil 2 c pr s a r up "1- of active conreceiving passage between the two heating coils. duOtOYS l2 one active tum-Side, and a group A primary object of our nti is to provide Hi of active conductors It for the other active an induction furnace apparatus of the type oleturn-side. The conductors of the groups are connected by end conductors l8 along one side scribed which requires no magnetic material for concentrating or otherwise guiding the heat-inof the strip-passage and end conductors 20 along the other. The heating coil 4, being similar,

ducing magnetic flux.

A further object of our invention resides in the Comprises Sp c roups 22 and 24 consisting of spaced parallel active conductors 26 and 23,

provision of heating-coil means on each side of the traveling material, which mutually cooperate resp ct y, Connected by e d-turns 30 and 32.

to provide, in effect, longitudinal magnetic flux The conductors of the group In of the heating for uniformly heating the material throughout. coil 2 are transversely aligned with and parallel An important advantage of our apparatus reto the conductors of the group 22 of the heating sides in the fact that the energy or power put coil 4. Similarly, the conductor-group M of the into the material can be controlled or adjusted heating coil 2 and the conductor-group 24 of the a 3 heating coil 4 are aligned on opposite sides of the strip 8, as more particularly shown in Fig. 2.

The coils are energized so that the current, at any instant, in a group of active conductors is in the same direction, but opposite in direction to the current in the group of conductors on the other side of the strip 8 and in the other group of active conductors of the same heating coil.

Referring to Fig. 2, the current directions are represented by dots to indicate current assumed to be flowing upwardly perpendicular to the plane of the drawing and by crosses to indicate current flowing downwardly perpendicular to the plane of the drawing. With current-flow in the active conductors as indicated by these dots and crosses, a magnetic field will be established in accordance with the flux lines 34, 36, 38 and 40 around the groups i8, i4, 22 and 24, respectively. It will be observed that flux lines flow longitudinally in the strip, these flux lines extending in opposite directions substantially from the center of the heating coils, between the groups of conductors of each.

Preferably, the heating coils are made of bare, hollow, copper tubing, so that they can be readily water-cooled, if necessary. As to the spacing between conductors of a heating coil, relatively wider spacing decr ases the magnetizing force for a given current, so that the spacing between the conductors should be as close as possible, limited only by the requirement for providing adequate insulation between the conductors. Generally, for ordinary use, one-eighth of an inch spacing or more should be satisfactory. The opposite coils should be spaced as close as possible, but suitable allowance should be made for mechanical requirements of clearance so that slapping or weaving of a strip or the like passing between the coils will not be detrimental to the heating apparatus.

The number of active conductors in a group will depend on the amount of heat necessary to put into the strip passing through the field length; and, in general, a greater number of active conductors requires a wider spacing between the groups of a heating coil. This spacing between groups of a heating coil should, in general, be about four times the spacing between the difierent heating coils on the opposite sides of the strip, so as to obtain a satisfactory fluxdistribution in opposite directions between the coils. If the groups of active conductors of a heating coil are too closely spaced, the magnetomotive forces produced by the energized coils tend to neutralize, so that the longitudinal flux will not be as great as it would be with a larger distance between the innermost active conductors of the two groups of a heating coil. The inner loop of a heating coil, which is the smallest in area, should preferably be as wide, or wider, than the width of the widest strip expected to be heat-treated. This means that all of the active conductors will be longer than the width of the strip, except perhaps for conductor to which the power source is connected. In general, the end-turn closest to the strip should be from two to four inches away from it to prevent nonuniform heating of the strip. With reference to Fig. 1, this distance between the innermost end-turn and the nearest edge of the strip is indicated at a. However, the active conductors of the heating coil may be less in length than the width of a strip, but in such case nonuniform heating transversely across the strip might result.

The heating coils should be energized from an alternating-current source capable of delivering the necessary heating power at higher frequencies, above several thousand cycles. Oscillating resonant circuit apparatus, such as a tubeoscillator or a spark-gap oscillator, is recommended. The frequencies may range as high as 500,000 cycles and above and still deliver the required power for heating the material, although no iron is used in the heating apparatus. In general, the most desirable frequency to use will depend on the physical properties of the material being heat-treated, the speed at which it is moving through the induction heating apparatus, and the required temperature rise.

In Fig. l, a tube oscillator equipment indicated in its entirety by the reference numeral 42 is shown in simplified form for energizing the heating coils. The tube-oscillator generator comprises a high-frequency circuit including power leads 44 and 45 to which the heating coil may be connected in difierent manners, for obtaining a current-flow, such as described, producing the oppositely directed magnetic flux portions in the strip portion between the heating coils.

In Fig. 3, the coils are connected in series. The outer conductor of the conductor group H! of the heating coil 2 is connected to the power lead 44, and the inner conductor of the conductor group [4 of this coil is connected directly to the inner conductor of the conductor group 24 of the heating coil 4; the outer conductor of the conductor group 22 of this coil being connected to the power supply lead 46. The aforesaid conductors are, of course, the terminating portions of the respective heating coils.

In Fig. 4, the heating coils are connected in parallel to the power supply leads 44 and 46. For this embodiment, the outer end of each heating coil is directly connected to the inner end of the other heating coil, and the connecting conductors 48 and 50, respectively, are connected to the power supply leads. The arrowheads in Figs. 3 and 4 indicate the current-direction at some instant when the supply lead 46 can be considered positive, so that the current will flow toward the supply lead 44.

In both Figs. 3 and 4, the heating coils are wound in the same direction, but obviously if they are wound in opposite directions the connections can be altered so as to produce the necessary current directions at any instant, in accordance with Fig. 2.

Where a heating coil extends completely across the strip, the end conductors between it active groups may take any desired form. In Fig. l, we have shown the heating coil generally in the form of a flat spiral or pancake so that the end conductors are in the same plane as the active conductors. This means that the active conductors will be of gradually greater length in a direction outwardly from the center of the coil. However, the active conductors may be made of the same length, and the end-turns or end conductors disposed one above the other, such as shown in Fig. 5, so that the tubing of which the upper heating coil is made will be bent upwardly from an active conductor of a group, then longitudinally, and then down again to an active conductor of the other group. The lower heating coil is, of course, similar but with the turns for the end connections extending downwardly from the strip-passage.

By using two pancake coils on opposite sides of the strip as described, a magnetizing force is obtained producing magnetic flux parallel to the strip, with the flux portions between the cooperative group of conductors on the two different heating coils in opposite directions at any instant. Each flux portion will induce approximately the same amount of heat if the heating coils are symmetrically constructed.

Such an arrangement, besides permitting ready insertion or removal of the strip edgewise, also aiiords an easy method of regulating the power put into the strip without requiring regulation of the tube oscillator through an expensive regulator of some kind. To vary the power to the strip, the two coils can be moved toward or away from it, normally to its face, or they may be hinged to increase or decrease their mutual coupling with the strip and their coaction with each other.

While we have described our invention in different forms and different embodiments, it is obvious that further changes can be made and embodiments utilized which embrace the teachings and principles of our invention.

We claim as our invention:

1. Coreless induction heating apparatus of a type described, comprising nonmagnetic means providing a flat work-passage having an open edge for receiving strip and the like, said means comprising a plurality of single-layer pancake heating coils on opposite sides of said work-passage, said heating coils having active substantially straight conductors spanning said workpassage, with conductors on opposite sides of the work-passage fleeing paralle1 and lying in planes substantially perpendicular to the work-passage, and means for energizing said heating coils for producing a longitudinal magnetic flux in opposite directions in said work-passage between said heating coils, the last said means comprising conductors for causing the current-flow in one of said heating coils to be clockwise at the same time that the current-flow in the other heating coil is counterclockwise.

2. Induction heating apparatus comprising coreless induction furnace-means providing a work-passage, said furnace-means comprising a pair of similar heating coils on different sides of said work-passage, each heating coil having an axis intersecting said work-passage and having active spaced substantially coplanar turn-sides on the same side of said work-passage, one of said heating coils having nested end-turns connecting the active-turns of the heating coil, said end-tums being farther from said work-passage than the associated active turn-sides, and a resonant circuit alternating-current generating source having a pair of power supply leads connected to said heating coils.

3. An induction heating apparatus of a type described, having nonmagnetic pancake-type coils of hollow piping providing a flat, narrow workpassage for heating elongated fiat material, said pancake-type coils of hollow piping comprising a plurality of similar groups of generally parallel coplanar spaced conductors extending transversely across said work-passage, there being a plurality of groups on one side of said workpassage and a plurality of groups on the other side of said work-passage, a group of conductors on one side of the work-passage being directly opposite a group in the other side, the spacing between groups on the same side of the workpassage being greater than that between adjacent conductors of such groups, means for passing alternating-current through said conductors so that 8 the current at any time will how in the same direction in the conductors oi the same group, but in opposite directions in juxtaposed groups.

4. An induction heating apparatus of a type described, having nonmagnetic means providing a fiat, narrow work-passage for heating elongated fiat material, said means comprising a plurality of similar groups of conductors, each group com prising a plurality of generally parallel coplanar spaced substantially straight conductors extending transversely across said work-passage, there being a pair of conductor-groups on each side of said work-passage, and associated conductorgroups on opposite sides thereof, the spacing between the groups on the same side of said workpassage being greater than the spacing between adjacent conductor-s of each such group, and means connecting the conductors of said groups so that current in the conductors of any one group will generally flow in the same direction, but opposite to the direction of the current in the conductors of the associated group on the opposite side of said work-passage and in the conductors of the other group on the same side of said work-passage.

5. An induction heating apparatus of a type described, having nonmagnetic means providing a flat, narrow Work-receiving passage for heating elongated flat material, said means comprising a plurality of similar groups of water-cooled conductors, each conductor being longer than the width of the material to be heated, each group comprising generally parallel coplanar spaced conductors extending transversely across said work-passage, there being a pair of conductorgroups on each side of said work-passage, and associated conductor-groups on opposite sides iereof, the spacing between the groups on the same side of said work-passage being greater than the spacing between adjacent conductors of each such group, and means for energizing the conductors or" said groups with high-frequency current so that the high-frequency current in the conductors of any one group will generally flow in the same direction, but opposite to the direction of the high-frequency current in the conductors of the associated group on the opposite side of said work-passage and in the conductors of the other group on the same side of said workpassage.

BENEDICT CASSEN. ROBERT M. BAKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Babat, Heat Treating and Forging, April, 1941, pages 193 and 194. Library.)

The Welding Engineer, July, 1943, page 43. (Copy in Div. 60.)

(Copy in Scientific 

